Brain development

“ Second, we know that the individual development of the brain is profoundly influenced by the internal secretions of certain ductless glands notably the thyroid. When this organ is not functioning properly the child's brain development is arrested. ”

“ We all believe in cerebral development according to what we call natural laws or causes, and in the parallel phenomena of mind; as also in the arrested and morbid action of brain-power by infractions of laws or by causes no less natural. In this sense we are all evolutionists. ”

“ We may, however, notice here that, as in his nervous organization, no distinctly new parts are discoverable, but only general growth and development, and especially vast increase in the size and working capacity of the cerebrum, together with improved lines of communication between the different parts of the brain, so in the psychical manifestations which this enlarged and better-developed brain exhibits, no faculties are discovered beyond what these various developments in structure render possible. Does man possess intelligence? ”

“ What we observe without, in this way, constitutes the sphere of objective psychology. But there is another capital source of a knowledge of mind, which comes from investigating the organic structures and functions by which it is manifested in all its grades and forms. We here study the brain and nervous system, tracing its evolution from the lowest germ to the highest development, and tracing the growth of the brain of man from its embryonic rudiments to the mature and perfected structure. ”

“ For, if we compare the different races of man, or the different species of animals, we find that, in general, the higher the cerebral organization attained, the longer the process of development. Men of great original power, having the most highly organized type of brain, may be expected to illustrate the most prolonged movement of mental growth. ”

“ Nothing in human development is more impressive than the origin of the cerebrum and its development by passing through successive stages which are counterparts in the main of the adult brains of other and lower animals. The alteration of a tissue-mechanism constructed in one way into a tissue-mechanism of a more complex nature, provides the most conclusive evidence of the reality of brain evolution, because the process of transformation actually takes place. ”

“ Is it not altogether probable that an intentional direction of the vital or mental forces to any particular portion of the brain will cause a development and activity in the corresponding portion of the brain of the offspring? ”

“ But there are certain functional activities which do tend so to alter the development of after-brains; certain novel or sustained activities which apparently result in the production of new correlated brain-elements or brain-connections, hereditarily transmissible as increased potentialities of similar activity in the offspring. ”

“ It is a legitimate inference that it is chiefly due to brain development, physiologically as a means of supporting the enlarged and correspondingly heavier head, which it would be difficult to carry in the horizontal position, and psychologically as the natural result of a growing intelligence and self-consciousness which seeks to lift the head and raise it to a position from which it can command its surroundings. ”

“ The foregoing details will be found to assist us in our criticism of the pretensions of the old phrenology as a basis for estimating "the mind's construction" and the mental habits of man. Primarily, let us inquire if development—that great criterion of the nature of living structure—lends any countenance to the idea that the brain is a collection of organs such as the phrenologist asserts it to be. The brain of man, like that of all other backboned animals, appears to begin its history in a certain delicate streak or furrow which is developed on the surface of the matter of the germ. ”

“ The development of a brain or cerebrum marks one important advance. The presence of this organ renders possible to the animal in varying degree what are called representations of objects, and the faculty of making such representations appears to be a condition precedent to the development of deliberation, volition, and purposive action as opposed to reflex or instinctive activity. ”

“ The growth of the brain is a matter of the first seven years almost wholly. It grows relatively little after that period; and until that is completed the physical apparatus of mind is not ready for educational interference. Without any such interference, and with merely the provision of conditions, physical and mental, for its spontaneous development, the brain of the seven year old will suffice for surprising things—so surprising that if their evolution were possible under any system of schooling practised before that date, we should applaud it as ideal. ”

“ For the two halves of the brain being once thus knit together, the progress of cerebral complexity is traceable through a complete series of steps from the lowest Rodent, or Insectivore, to Man; and that complexity consists, chiefly, in the disproportionate development of the cerebral hemispheres and of the cerebellum, but especially of the former, in respect to the other parts of the brain. ”

“ Mental Development.—We note that at birth the brain is mindless, and that the brain-cells, which are the vehicle of the mind, undergo their greatest development during childhood from stimuli coming from without the body. The brain-cells possess infinite possibilities and potentialities. They are developed from the stimuli from without through the eyes, ears, touch, taste, and smell. There is another series of constant impressions which are received from within the body, and these come from the muscles. ”

“ Those who contend that knowledge results wholly from the experiences of the individual, ignoring as they do the mental evolution which accompanies the autogenous development of the nervous system, fall into an error as great as if they were to ascribe all bodily growth and structure to exercise, forgetting the innate tendency to assume the adult form. Were the infant born with a full-sized and completely-constructed brain, their position would be less untenable. ”

“ Early forms of life had no brains to speak of. They received impressions and transmitted them in expressions without check or discrimination. With the development of more complex organisms and their more complex activities came the accompanying complexity of brain, which could co-ordinate those activities to the best advantage. Action is the main line of growth. Conditions press upon all life, but life is modified through its own action under given conditions. And the relative wisdom and success of different acts depend on the brain power of the organism. ”

“ There is, according to the suggestion put forward in this chapter, an interneural evolution, leading to an harmonious development of the neuroses in the individual brain. But this special evolution of the brain is nowise independent of the more general evolution of the body. The human being, as an organism, is still subject to natural elimination and human selection. Elimination through the action of surrounding physical conditions, although it has played some part in the evolution of man, is not a factor of the first importance. ”

“ In the long process of development of animal organisms out of one another there come to be, it is said, higher and higher degrees of intelligence, as the nervous system becomes more and more capable of complex impressions, until we arrive at the consummate physical organization and the supreme intelligence of the human race. The physical organization is open to our examination, and we find the human brain divided into cerebral masses, with ganglia of sensory nerves extending to the external sensory organs. ”

“ This curious state of things is probably only accidental to the present stage of development of the human mind, and may, at any time, be rectified by perhaps either a slight rearrangement of that slender network of nerves upon which depends our faculty of thinking, or the joining together of a few microscopical filaments attached to the cells in the grey cortical layer, or even a single bridge thrown across from one convolution to another of the brain; a very slight alteration would open up to our consciousness the present existence of the future. ”

“ As soon as physiologists had discovered that all the faculties of the intellect, however originating or upon whatever exercised, were functions of a material organism of brain, absolutely dependent upon its integrity for their manifestation, and upon its growth and development for their improvement, it became apparent that the true office of the teacher of the future would be to seek to learn the conditions by which the growth and the operations of the brain were controlled, in order that he might be able to modify these conditions in a favorable manner. ”

“ Again, a progressive alteration of the brain as the result of diseased growth causes the mind to grow dim and incapable. Sometimes infants are born which are so deficient mentally as to be idiots, and an examination of the brain in such a case reveals certain correlated defects in physical organization. These and similar facts form the basis for the dictum that the development and evolution of the brain mean the growth and evolution of human intellect. ”

“ Does any one in his senses believe that an ape-human animal developed one-third of the normal human brain in 375,000 or 750,000 years, when it took 59,250,000 years to develop two-thirds of the brain? If one-third of the normal brain developed in the last 750,000 years, the rate of development must have been 39.5 times as great as in the preceding 59,250,000 years. If one-third developed in the last 375,000 years, the rate of development must have been 78 times as rapid as in the preceding 59,625,000 years. ”

“ A peculiar fact relating to these convolutions is observed by all anatomists: mental [pg 99] development is always accompanied by an increasing dissimilarity between their proportional size.
The cerebral hemispheres may be injured or lacerated without any pain to the patient. The effect seems to be one of stupefaction without sensation or volition. A well-developed brain is a very good indication of intelligence and mental activity. That the cerebrum is the seat of the reasoning powers, and all the higher intellectual functions, is proved by three facts. ”

“ We propose to speak of four constitutional variations entitled to separate consideration; the lymphatic, the sanguine, the volitive, and the encephalic. The brain controls all the voluntary, and modifies the involuntary functions of the body. A particular cerebral development modifies the functions of all the bodily organs, and thus tempers the constitution. We shall, therefore, base our classification of temperaments upon the mental and physiological characteristics, which are portrayed by cerebral development. Such an arrangement is illustrated by Fig. ”

“ There are whole areas of brain-cells which are evolved only through the efforts of hand and eye, for it is the mind at last that directs all our energies. The development of brain and body go together—manual work is brain-work. ”

“ All these conditions concur in determining the quality of the cerebral tissues. In its ontogenetic evolution, for example, the brain does not merely increase in volume, and its development is not limited to attaining a definite morphology ”

“ On the contrary, he sees that in the vertebrates those parts of the brain which physiological research and pathological experience prove to be the seat of the higher mental activities keep pace, in their comparative development, with the growth of these activities. Where mental capacity makes the immense leap from the anthropoid apes to man which is indicated by the power of speech, we find a corresponding leap in cerebral mass. ”

“ The more recent development of the mind has been in its intellectual powers, while its physical aptitudes have somewhat declined. This has not yielded any marked increase in the dimensions of the brain, but it may have had a decided effect upon the proportion of its parts, the regions of the cerebrum devoted to intellectual activity probably increasing at the expense of the motor and sensory regions, while the convolutions may have grown considerably more complicated. ”

“ Each infant of the human race, to whom has descended this improved and perfect brain, has latent in that organ a high capacity for intelligence. This it begins to exercise and strengthen and further compli [Pg 519] cate as life goes on, and at the end of twenty or thirty years the individual brain is fully developed, and this development, or capacity for development, the individual bequeaths with minute additions, principal and interest, to future generations. In different races of men the cubic bulk of the brain varies greatly, according to the size transmitted from ancestors ”

“ Again, when it is shown from numerous cases that the highest average weights of brain in both sexes occur not later than twenty years of age, it appears a more legitimate inference to trace to exceptional cerebral development towards the period of adolescence, the mortality which rendered available so many examples of unusually large or heavy brains, than to assume that the normal healthy brain begins to diminish at that age. ”

“ It may be inferred from the number of cases pointing to an early attainment of the highest average brain-weight, not that the brain differs from all other internal organs of the human body in attaining its maximum before the period of puberty; but that physical as well as mental vigour are dependent on the maintenance of a nice equilibrium between the brain and the other organs while in process of development. ”